+1 hereWhat did Christ say we should do in such a situation?
Matthew 18:15-17 -
15. Moreover if thy brother shall trespass against thee, go and tell him his fault between thee and him alone: if he shall hear thee, thou hast gained thy brother. 16. But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established. 17. And if he shall neglect to hear them, tell it unto the church: but if he neglect to hear the church, let him be unto thee as an heathen man and a publican.
The Resurgam translation and application of that passage: I'd go talk to the guy and let him know exactly what you felt from his looks at the two of you and exactly what you overheard. Don't leave anything out - be honest. If he convinces you that you're overreacting, great. If he acts the least bit sketchy and especially if he is confrontational or levels any veiled threats, take one or two more established and respected men in the church with you to talk to him again. That way it's more than just your word against his, and if he's really a nut the other guys will catch on. If he doesn't repent, you and, according to Christ, the entire church are obligated to shun the man. No more coming to Bible study to ogle your girl and fantasize about stabbing yall.
Then I'd go get a restraining order against him and watch my back (and hers) double-time. The restraining order may help in court if you ever have to prevent him from harming y'all.